Metal-Oxide Semiconductor Field Effect Transistors (“MOSFETS”) are a common type of power switching device. A MOSFET device includes a source region, a drain region, a channel region extending between the source and drain regions, and a gate structure provided adjacent to the channel region. The gate structure includes a conductive gate electrode layer disposed adjacent to and separated from the channel region by a thin dielectric layer. When a voltage of sufficient strength is applied to the gate structure to place the MOSFET device in an on state, a conduction channel region forms between the source and drain regions thereby allowing current to flow through the device. When the voltage that is applied to the gate is not sufficient to cause channel formation, current does not flow and the MOSFET device is in an off state.
In the past, the semiconductor industry used various different device structures and methods to form MOSFETS. One particular structure for a vertical power MOSFET used trenches that were formed in an active area of the MOSFET. A portion of those trenches were used as the gate regions of the transistor. Some of these transistors also had a shield conductor that assisted in lowering the gate-to-drain capacitance of the transistor. Lowering the gate-to-drain capacitance of the transistors increases the transition rate of their drain-to-source voltage during turn-on and turn-off of the transistors. A low gate-to-drain capacitance reduces the switching power losses of the MOSFET, and hence results in increased efficiency in some applications. However, in applications in which the MOSFET serves as, for example, a high side FET, where its source is coupled to the drain of a low side FET to form a switch node, the increased transition rate during turn-off may lead to ringing at the switch node. The ringing becomes more pronounced in packages having a high source inductance and can cause the systems in which the transistors are used to malfunction and dissipate a large amount of energy.
Accordingly, it would be advantageous to have a semiconductor component and a method for forming the semiconductor component that predictably and reliably optimizes the gate-to-drain capacitance of a FET to achieve a good trade-off between efficiency and switch node ringing. It would be of further advantage for the semiconductor component to be cost efficient to manufacture.
For simplicity and clarity of the illustration, elements in the figures are not necessarily drawn to scale and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of a MOSFET, or an emitter or a collector of a bipolar transistor, or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of a MOSFET or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-channel devices, or having certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. The use of the words approximately or about means that a value of an element has a parameter that is expected to be very close to a stated value or position or state. However, it is well known in the art that there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variance from the ideal goal as described. For clarity of the drawings, doped regions of semiconductor component structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions generally may not be straight lines and the corners may not be precise angles.
In addition, the description may illustrate a cellular design (where the body regions are a plurality of cellular regions) or a single body design (where the body region is comprised of a single region formed in an elongated pattern, typically in a serpentine pattern or formed in a plurality of stripes). However, it is intended that the description is applicable to both a cellular implementation and a single base implementation.
In some instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to obscure the present disclosure. The following detailed description is merely exemplary in nature and is not intended to limit the disclosure of this document and uses of the disclosed embodiments. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding text, including the title, technical field, background, or abstract.